Electronic devices and components generate heat and in many applications, the heat needs to be effectively dissipated for the device function. Polymeric resins have extremely low thermal conductivity in comparison with other inorganic substance such as a metal material, and therefore, it is difficult to release the generated heat. There have been several attempts to obtain a highly thermal conductive resin composition by incorporating fillers with high bulk thermal conductivity.
Generally, fillers can be divided into three types: electrical conductive, semi-conductive and electrical insulation. Electrical conductive fillers include metals such as Au, Ag and Cu for example and metal alloys. Graphite and carbon fiber can be regarded as semi-conductive fillers, since electrical insulation property is reduced when they are used. Therefore, electrical conductive and semi-conductive fillers are not suitable for electronic device applications, even they have very high thermal conductivity.
Electrical insulation fillers are widely used in light-emitting diode (LED) technology for providing high thermal conductivity and good electrical insulation properties. Examples of such fillers are AlN, BN, Si3N4, Al2O3 and diamond. AlN and BN are widely considered to have high bulk thermal conductivity, however, the application of AlN and BN is limited due to their hydrolysis reaction and the environmental hazards. On the other hand, diamond provides good physical properties as well as extremely high thermal conductivity, however, high cost creates a problem in wider use. Al2O3 provides good thermal conductivity as well as other physical properties and the costs are reasonable.
Heat dissipation remains one of the big challenges for LED chips. Heat dissipation depends on thermal conductivity of die attach paste between the chip and the substrate.
During recent developments in the electronic industry, the chips for LED applications have became smaller and thinner, which requires that the bond line thickness of die attach paste need to be evermore thinner. This creates limits for the filler's particle size as the fillers with large particle size hinder the formation of thin bond line thickness of die attach paste. Obviously, the fillers with small particle size decrease the bond line thickness of die attach paste. However, small particle size does not necessary provide adequate heat dissipation. In general high thermal conductive fillers, such as spherical alumina particles with lower particle size cannot meet high thermal conductive requirement while larger particle size cannot meet the requirement of lower bond line thickness for die attach paste. More specifically, for example small spherical Al2O3 filler particles do not meet the thermal conductivity requirement for LED applications.
In addition, anti-yellowing properties have become very important feature for die attach pastes used in the LED application as die attach paste is exposed for high temperatures for a long time. Above mentioned small spherical Al2O3 filler particles do not have very good anti-yellowing properties either.
Therefore, it is objective of the present invention to provide a die attach paste with good heat dissipation and anti-yellowing properties in combination with capability to form thin bond line thickness.